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Chapter Electronic and Optical Transmission © N. Ganesan, Ph.D. , All rights reserved. Chapter Objectives • Describe the basic transmission features of electronic and optical transmission – Variation in the voltage of digital signals etc. • Briefly discuss the electronic-to-optical and optical-to-electronic interfaces Chapter Modules • Basics of electronic transmission • Basics of optical transmission • Fiber optic connections Module Basics of Electronic Transmission © N. Ganesan, Ph.D. , All rights reserved. Simple Digital Encoding of Data Voltage 1 0 0 0 0 0 1 Transmission of A Pulse Pulse Duration TIME A -------------> ASCII -----------> 1000001 Summary of Digital Electronic Transmission Square waves are coded based on voltages to represent either a one and a zero. A Code and generate Electronic signals B Receive and Decode electronic Signals Both points operate under the same rules and guidelines for effective communication. An Early Introduction to the Concept of Protocol • Communication protocol is a set of rules and guidelines for transmission • A simple protocol that applies to the previous example is as follows: – 0 = 0.05 Volts – 1 = 0.1 Volts – Pulse duration is 1 nanosecond • In practice, the protocols are much more sophisticated An Example of a Widely Used Protocol • TCP/IP – Transmission Control Protocol/Internet Protocol – De facto protocol of the Internet – TCP/IP is a stack of protocols • Some examples of protocols in the TCP/IP stack – UDP, SMTP, POP3 etc. End of Module Module Basics of Optical Transmission © N. Ganesan, Ph.D. , All rights reserved. Optical Transmission Optical Transmission Light Pulse Origin Destination Pulses of different wave lengths (frequencies) are used for representing 0s and 1s. Wave Length • Wave length is inversely proportional to frequency – Wave length = 1/Frequency • Higher the frequency, the shorter the wave length Fiber-Optic Transmission Characteristics • Signal encoding (0 and 1) can be based on light rays of different wave lengths • Possible light sources are, for example: – Laser – Light Emitting Diode (LED) • Conversion from light to electricity – Photo Electric Cell Characteristics of Optical Transmission in a Fiber • In general, the laws of physics say that light travels along a straight line • In optical fibers, however, light travels along the path of the fiber Example of Path of Propagation of Light Waves in Fiber Cables Tips glow Light travels along the path of the fiber Fiber Vase Ornament Light Source Optical Transmission In Fiber Light bounces and travels along the fiber Optical Transmission Alternatives • Multimode Step Index – Lower speed optical transmission • Multimode Graded Index – Intermediate speeds of transmission • Single Mode – Higher speed in transmission Optical Transmission Alternatives Cont. Multimode Step Multimode Graded Single Mode Light Propagation Source: Corning Tutorial Fiber Properties • Glass (silicon) is used in most cases as the material for producing fiber strands • Low cost plastic fibers are also available at present • However, the connections involving plastic fibers are limited by distance compared to silicon fibers Rule of Thumb • Purer the fiber, the smaller the loss in signal strength and hence, further the light travels Multi-Mode Fiber Source: Corning Tutorial Single Mode Fiber Source: Corning Tutorial Example of Fiber Cables Fiber Connections • For full duplex transmission there are two connectors in the case of fiber connections – Transmitting connection is denoted as TX – Receiving connection is denoted as RX End of Module Module Fiber Optic Connections © N. Ganesan, Ph.D. , All rights reserved. Optical-to-electronic Conversion Light Optical Signals PhotoElectric Cell Electricity Electronic Signals Electronic-to-optical Conversion Light Light Emitting Diode (LED)/ Laser Electricity How Fiber Works: Source: Corning Tutorial Electro-Optical Fiber Interface Source: Black Box Example in Extending the Communication Link Between Two Computers Computer/ Comm. Elect. System A Optic. Fiber Interface Elect. Computer/ Comm. System B Typical Use Of Optical Technology • Extending the distance between two communication points – Line drivers • Telecommunications – Long distance telephone trunks • Large-scale network backbones – FDDI • Internetworking – Connection between switches Fiber Connection for Extending a T1 Line Connection Multimode Fiber cable 1.5 Miles at 256 Kbps and 3 miles at 64 Kbps. Source: Black Box Fiber Connection for Extending LAN Connection Up to 31 miles. Speeds from 56-2048 Kbps. Source: Black Box Fiber Line Driver Fiber cable port. Source: Black Box Fiber Connection Between Switches Fiber Connection References • Corning Library • Corning Tutorial – This can be downloaded and played • Locally hosted fiber-optic reference on the reference page of this web (Week 6) • Other useful references can be obtained from the web as well Key Words • • • • • • • • Pulse duration Square wave Protocol TCP/IP Wave length Laser and LED Photo Electric Cell Multi-mode and single mode fiber Key Words (Continued) • Fiber transmission advantages • ST and SC connections • RX and TX • Media interface • Fiber usage – Telecommunications, campus backbone, FDDI and Internetworking End of Module End of Chapter End of Module END OF CHAPTER